Devices (and methods) for regulating the speed and/or acceleration of a vehicle are known by the name of "Tempomat." Such a device can be supplemented by a sensor that can detect other vehicles driving in front of the vehicle, plus any obstacles in the direction of travel. Thus, the device may take into account not only its own internal traffic parameters, but also ambient parameters in the regulation of vehicle speed. Such devices are known in general as adaptive or dynamic road speed governors, and are also referred to as adaptive cruise control (ACC). A basic description of such a device is found, for example, in the article "Adaptive Cruise Control--System Aspects and Development Trends" by Winner, Witte et al., published at SAE 96 of Feb. 25-29, 1996, Detroit.
The driver of a vehicle having such an ACC unit can preselect a desired speed vset. If the road is free of slower-moving vehicles and any obstacles in the area in front of the vehicle, the ACC unit adjusts the speed vF of the vehicle to this selected desired speed. However, if there are slower-moving vehicles in the path of the vehicle being regulated, the vehicle will adjust to the speed of the slower-moving vehicle. A minimum distance, which can also be set, is maintained. Therefore, in heavy traffic, the ACC unit may establish for a long period of time a speed vF which is lower than the desired speed vset originally selected by the driver. Accordingly, with such an adaptive cruise control, it is necessary to first display for the driver the desired speed which the driver has set.
One example of how this can be accomplished is described in the above-mentioned article. In particular, a known speedometer is provided with additional LEDS in the area of its speed scale, i.e., above or below the individual scale values. On of the additional LEDs displays the selected desired speed. The prevailing speed is indicated by a speedometer needle in a known manner. One problem in this regard is that speed vFA displayed as the actual speed is usually higher than the actual instantaneous speed vF. This deviation .DELTA.v is known as the speedometer lead and is system-induced, mainly because of statutory requirements. Problems arise when the path in front of a vehicle operating on cruise control is clear and thus the vehicle operating on cruise control is traveling at the set speed vset. If the speed is set at 100 km/h, for example, the vehicle operating on cruise control will also travel at an actual speed vF of 100 km/h, disregarding individual tolerances. Then, because of the speedometer lead, a speed vFA of 105 km/hr, for example, will be displayed. At the same time, a display shows the driver that his selected desired speed is 100 km/h. This discrepancy gives the driver the impression that his vehicle is driving too fast and that perhaps the cruise control is just malfunctioning.
This disadvantage can be eliminated by taking into account speedometer lead .DELTA.v in setting a desired speed. However, since the speedometer lead can vary from one vehicle to the other and thus especially from one manufacturer to other, this requires a very high application expense in setting up and adapting an ACC unit to a vehicle.